In printers with a moving carriage, the wider the media fed through the printer, the greater the distance traveled by the carriage. Typically, the carriage travels along a carriage rod mounted on a backbone, which is a support surface, typically made from sheet metal. Under the moving carriage, media is supported during printing by a support surface generally referred to as a platen.
When the print width of a moving carriage printer is increased, the stiffness of each widened element is significantly decreased. When the lengthened elements must support a transverse load, significant bending deformation can result. This can adversely affect printing performance.
The backbone and the platen need to support transverse loading, for example when they are required to pinch print media against a rotating drive roller. The total amount of transverse loading to be provided by the backbone and platen depend upon the width of the media. If a printer is designed to handle wider media, the backbone and platen must proportionately provide a greater amount of transverse loading in order to provide a uniform amount of pinch force across the entire width of the media. This linear increase in transverse loading results in an exponential increase in stress tending to bend the backbone and the platen. The bending can result in inconsistent pinch force across the width of the media and may result in a complete loss of pinch force at the center of the media. The bending of the backbone can also result in non-uniformity in the distance between the carriage and the media during printing.
In order to compensate against increased transverse loading, the thickness of the sheet metal can be increased, or stiffer materials can be selected reducing the amount of bending. For example beryllium or tungsten steel alloy can be used instead of standard carbon steel to form the backbone and the platen. Changing the shape of the backbone and the platen can also reduce bending. However, such solutions can adversely affect one or more of the printer size, weight and cost of materials.